Segment Information - Schedule of Segment Reporting Information by Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2017
Segment Reporting Information [Line Items]
Total financing revenues	$ 2,647	$ 2,496	$ 5,245	$ 4,954
Depreciation on operating leases	1,719	1,683	3,400	3,272
Interest expense	452	297	900	604
Net financing revenues	476	516	945	1,078
Insurance earned premiums and contract revenues	221	199	437	392
Investment and other income, net	55	42	102	81
Realized gains (losses), net on investments in marketable securities	1	70	42	83
Net financing revenues and other revenues	753	827	1,526	1,634
Expenses:
Provision for credit losses	127	161	212	213
Operating and administrative expenses	337	317	650	596
Insurance losses and loss adjustment expenses	102	91	216	180
Total expenses	566	569	1,078	989
Income before income taxes	187	258	448	645
Provision for income taxes	70	95	166	241
Net income	117	163	282	404
Total assets	120,100	115,793	120,100	115,793	$ 119,635
Intercompany Eliminations [Member]
Segment Reporting Information [Line Items]
Total financing revenues	0	0	0	0
Depreciation on operating leases	0	0	0	0
Interest expense	(3)	0	(6)	0
Net financing revenues	3	0	6	0
Insurance earned premiums and contract revenues	0	0	0	0
Investment and other income, net	(3)	0	(6)	0
Realized gains (losses), net on investments in marketable securities	0	0	0	0
Net financing revenues and other revenues	0	0	0	0
Expenses:
Provision for credit losses	0	0	0	0
Operating and administrative expenses	0	0	0	0
Insurance losses and loss adjustment expenses	0	0	0	0
Total expenses	0	0	0	0
Income before income taxes	0	0	0	0
Provision for income taxes	0	0	0	0
Net income	0	0	0	0
Total assets	(1,104)	(979)	(1,104)	(979)
Finance Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total financing revenues	2,647	2,496	5,245	4,954
Depreciation on operating leases	1,719	1,683	3,400	3,272
Interest expense	455	297	906	604
Net financing revenues	473	516	939	1,078
Insurance earned premiums and contract revenues	0	0	0	0
Investment and other income, net	36	24	68	47
Realized gains (losses), net on investments in marketable securities	0	76	0	87
Net financing revenues and other revenues	509	616	1,007	1,212
Expenses:
Provision for credit losses	127	161	212	213
Operating and administrative expenses	259	242	492	452
Insurance losses and loss adjustment expenses	0	0	0	0
Total expenses	386	403	704	665
Income before income taxes	123	213	303	547
Provision for income taxes	47	80	112	205
Net income	76	133	191	342
Total assets	116,463	112,355	116,463	112,355
Insurance Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total financing revenues	0	0	0	0
Depreciation on operating leases	0	0	0	0
Interest expense	0	0	0	0
Net financing revenues	0	0	0	0
Insurance earned premiums and contract revenues	221	199	437	392
Investment and other income, net	22	18	40	34
Realized gains (losses), net on investments in marketable securities	1	(6)	42	(4)
Net financing revenues and other revenues	244	211	519	422
Expenses:
Provision for credit losses	0	0	0	0
Operating and administrative expenses	78	75	158	144
Insurance losses and loss adjustment expenses	102	91	216	180
Total expenses	180	166	374	324
Income before income taxes	64	45	145	98
Provision for income taxes	23	15	54	36
Net income	41	30	91	62
Total assets	$ 4,741	$ 4,417	$ 4,741	$ 4,417